Telegraph repeater



3 Sheets-Sheet 2 R. B. HEARN TELEGRAPH REPEATER Filed June 26, 1940 Oct.2l, 1941.

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BV 71, AfTO/MEV Oct. 2,1, 1941. R. B. HEARN TELEGRAPH REPEATER FiledJune 26, 1940 3 Shets-Sheet 3 .lllllll www /NVEA/TOR REWE/WN A TTG/PNE Vtral .repeater concentration.

Patented Oct. 21, 1941 'UNiTEo sTATEsPArENT ori-ICE TELEGRAPH REPEATERRichard B. Hearn, Hollis, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication June 26, 1940,*ser'ia`1No. 342,431 11 Claims. A `(C1.irs-73) This invention is a new telegraph repeater and, particularly, aterminal telegraph repeater for use in interconnecting a four-wiretelegraph circuit with inverse neutral circuits Vor hub circuits, asthey are known in the art.

An object of the invention herein is the pro vision of an improvedtelegraph terminal repeater for 'use in interconnecting a fourwiretelegraph circuit with inverse neutral telegraph circuits. y

.A further object of the invention v.herein is the provision of aterminal repeater. which may,

at a lirst time, interconnect a four-wire telegraph circuit, and a groupof telegraph circuits associated together to form a single hub circuit,toi' provide .half duplex operation lbetween the inverse neutral circuitand the four-wire `circuit; and which terminal repeater may beconditioned so as toserve at a second time between the fourwire circuitand two groups of telegraphl circuits; associated together in two hubcircuits, `tovprovide full duplex operation .between the inverse.neutral circuits and the four-wire circuit.-

By full duplex operation, in this application,

is meant simultaneous two-way communication'V only. It does not mean`simultaneous two-way communication over a single wire. It is notpossible to transmit in two directions simultaneously through the hub ofa .single inverse vneu- As .is well understood by those skilled .in thetelegraph art, when a group of circuits `are associated through a singlehub in an inverse neutral repeater concentration, while the markingcondition prevails, all legs radiating from a hub are terminated inbattery of the same vpolarity and magnitude. No current Vflows in any ofthe legs for this condition. In order to transmita spacing signal,ground is connected to the leg associated with the particular stationwhich is sending. Current thereupon ows from negative battery in each ofthe spokes or legs of the hub which is at the time receiving, toward thecommon hub point and through said point, to ground on the single sendingleg. A receiving `relay is thereupon operated in each branch. which isreceiving, transmitting a spacing signal to its respective facility.

In order to provide simultaneous two-way communication in inverseneutral telegraph repeater systems, it is necessary to provide twoseparate independent hubs. Each party associated in such a system whensimultaneous twoway communication is provided, must have -ac-y filo cessto two separate hubs through two separate inverse neutral repeaters.

In the inverse neutral repeater system disclosed herein, means areprovided for interconnecting an inverse neutral repeater concentrationgroup, which is established at a iirst telegraph central terminal,through a four-wire telegraph trunk circuit, toga distant telegraphterminal.A The four-wire telegraph trunk is Vequipped with a specialinverse neutral repeater to enable it torbe connected to the inverseneutral concentration lat the first telegraph central terminal', Thefour-wire telegraph trunk disclosed herein is arranged also so that it`may be connected either to a single hub at the lirst telegraphterminal, or to two separate hubs at the rst telegraph terminal. Whenthe trunk is conconnected to the single hub at the first telegraphterminal, any party joined to the hub at the rst telegraph terminal maytransmit simultaneously to all other parties connected into the hub atthe rsttelegraph terminal as well as to Ythe party or Aparties that maybe connected at the distant central terminal by vmeans of thetransmitting loop of the four-wire trunk which extends to the distantcentral terminal. Similarly any party joined to the trunk at the distanttelegraph terminal, may, at another time, transmit from the distantterminal over the other loop of the four-wire trunk, through the singlehub at the rsttelegraph central terminal to all parties connected to thesingle hub at the rst telegraph central terminal.

vfor simultaneous two-way operation.

. minal, all of its four wires, two -of which are are `ranged to form atransmitting loop and the other two a receiving loop, are required ineach form Vof operation. Simultaneous two-way communication through twoinverse neutral repeater concentration hubs 'and the four-wire .trunkcircuit will be called full duplex operation in this application. Y Y

A feature of this invention is its arrangement so that thePside of therepeater arranged for concentration, for conditioning the repeaterherein to operate as a half duplex repeater and which switchingarrangement functions, when the repeater herein is connected to two hubconcentrations, for conditioning the repeaterA herein to operate as afull duplex repeater.

A further feature of the invention is an arrangement for reversing abattery connected in Y series in the two conductors serving as thetransmitting circuit on the four-wire side of the repeater for thetransmission of marking and spacing signals.

A further feature of the invention is the use of an auxiliary receivingrelay, controlled by the receiving relay in the two receiving conductorsin the four-wire side of the circuit, which auxiliary receiving relayoperates to connect alternately to the hub point battery of thel samepolarity as is connected to each hub leg as a-marking signal and groundas a spacing signal.

A further feature of this invention is an arrangement wherein theswitching device, which operates when the repeater herein is conditionedfor half duplex operation, extends the transmitting path from theinverse neutral circuit through a winding on the auxiliary receivingrelay, so that theV auxiliary receiving relay may be controlled, inresponse to a break signal from the inverse neutral circuit to stop thetransmission of signals from the four-wire side of the circuit into theinverse neutral circuit.Y

These and other features of the invention will be made apparent from thedetailed description of the invention hereinafter when"read withreference to the associated drawings.

Fig. 1 shows a terminal repeater of the' in vention herein designed toconnect inverse neutral telegraph circuits arranged at its left to afourwire telegraph circuit.

Fig. 2 shows the manner in which-the repeater per Fig. 1 isinterconnected through a hub concentration to provide half duplexservice.

Fig. 3 shows the manner in which.'- the repeater per Fig. 1 isinterconnected through two hubs to provide full duplex service.

Ihe concentration jack circuit and the leg multiple circuit, shown inFigs. 2 and 3, are indicated only schematically. They are not shown incomplete detail as they are not a part of this invention and anunderstanding of their operation is not necessary to an understanding ofthe present invention. The various telegraph legs are arranged into hubgroups by means of the concentration jack circuits. The concentrationjack circuits and the leg multiple circuit provide means for exiblyconnecting the repeater of Fig. 1 to various hub concentrations asrequired. It is to be understood that the repeater per Fig. 1 may beterminated in the jack shown in the leg multiple circuit, frim whichjack it may be flexibly connected as required to an inverse neutral orhub concentration, or the repeater per Fig. 1 may be associated with oneor more inverse neutral concentrations through the concentration jackcircuit as indicated.

Inverse neutral or hub repeaters are described in detail in Patents2,056,277, F. S. Kinkead et al., October 3, 1936; 2,069,251, F. S.Kinkead, February 2, 1937; and 2,069,224, G. C. Cummings, February 2,1937.

As described in these patents inverse neutral repeaters are joined in acommon point from which the legs of the various connecting circuitsradiate. For the marking condition all legs are terminated in battery ofthe same polarity and same potential. For the spacing condition groundis connected to a particular leg to operate a receiving relay in each ofthe other legs in the same inverse neutral concentration simultaneously.Each group of repeaters associated through a single hub, as is wellunderstood, is capable of transmitting in one direction only Y at anyone time. That is to say, any one station associated in the hub maytransmit signals through the hub point to all of the other stationssimultaneously. ^When full duplex service is providedV it is necessaryto provide two diiferent hub circuits, one for transmitting and one forreceiving. vThe circuit of the present invention is designed so that itmay function either on a half duplex or on a full duplex'basis.

FULL DUrLE/x OPERATION Refer to Figs. 1 and 3.

In order to provide full duplex service it is necessary to provide twoseparate hub circuits, as indicated in Fig. 1 and Fig. 3. The threeleads 46, 41 and 48 extending from the repeater herein toward the leftof the drawing per Fig. 1 into the box marked Leg multiple circuit arearranged so that half duplex service or full duplex service may beprovided by means of the repeater of the invention herein.

When half duplex service is provided, as indicated when Fig. 1 isconnected to Fig. 2, only one hub circuit is required to be connected tothe left-hand side of the repeater herein. For full duplex operation, asindicated when Fig. 1 is connected to Fig. 3, a hub repeater isconnected to both of the main transmitting conductors extending to theleft of Fig. 1. When half duplex service is provided only one of themain transmitting conductors extending to the left of the figureperforms any function and it is connected to a single hub concentration.The purpose of the third lead extending to the left of the figure is tocondition the circuit herein for full duplex or half duplex operation.When half duplex operation is required ground is connected from relaycontacts in the leg multiple circuit to the lead extending through thewinding of relay l. This disconnects the lower transmission lead 41which functions only when full duplex service is required and conditionsthe circuit herein for half duplex operation.

It is to be understood that the circuit herein extends to hub repeatersthrough switching circuits to Vfacilitate the connection of the circuitof the invention herein with the other hub repeaters, but since theseswitching circuits form no part of the present invention they will notbe shown in detail. It should be understood, however, that for themarking condition for full duplex operation each of the maintransmitting leads is connected to the common point of a hub circuit.From the common hub point the circuit extends to the legs of anotherrepeater.

The transmitting leg of each repeater vconnects to the receiving leg ofthe other repeater. Pro- @esegesi `vision ismade for connectingadditional to eitherhub, if required.-

For full duplex operation since both `main transmitting leads 46 land 41extending to the left of Fig. 1 are required, relay I, Fig. 1, is'gtoremain in the unoperated condition as shown. Therefore, the circuitextending from battery through the winding of relay I over conductor 48to the left of Fig. l into Fig. 3 is open for this condition through theoperation of a relay in the leg multiple circuit (not shown) whichdisconnects ground from conductor 48.

A circuit may be traced from battery 2, Fig. 1, through resistance 3 andthe top windings of relays 4 and 5 to ground. This circuit providesvbiasing current to hold the armatures of relays 4 and 5 in theirmarking positions as indicated. A circuit may also be traced frombattery 2 through resistances 6 and 'I, through the bottom windings ofrelays 4 and 5, through the righthand armature and break contact ofrelay I,

through resistance 23 and the bottom main transmitting lead 4'I towardthe'left of Fig. 1 into Fig. 3 where it is connected through a legmultiple circuit and a concentration jack circuit in Fig. 3 to hub pointI, from which it extends through the armature and marking contact ofrelay I in the teletypewriter station transmitting loop repeater andthrough the top winding of loop repeater relay 2 to negative battery.Since `each one of the leads connected to the hub terminates in batteryof the same polarity as that of battery 2 in Fig. 1, r-no current williiow through the bottom windings of relays 4 and 5,

'so that the current through the top or biasing winding will beunopposed for the marking condition.

A circuit may also be traced from batteryr, Fig. 1, through resistances8 andl 9, through the left-hand break contact and armature of relay" I,through the left-handV or marking contact and armature of relay I andover the top Vmain transmitting lead 455 toward the left of Fig. '1

into Fig. 3. YLead 46 is connected in the same manner as 4l to a hubpoint, hub 2, from which it extends also to negative battery, in looprepeater 2, which is connected to the receiving loop of a tcletypewriterstation circuit. Therefore, no current will ow in this path for themarking condition. i

A circuit may also be traced from the positive terminal of the batteryI5, through resistance I6, through the right-hand or marking contact andarmature of relay 5, through the bottom windings cf induction coils I3and I2 and the bottom windings of repeating coil I I, over the lowerlead of the top pair of conductors extending to the right of Fig. 1,which are the transmitting leads 'of the four-wire circuit, through thereceiving device at the distant terminal and thence returning over thetop lead through the top winding of repeating coil II and the topwindings of induction coils I2 and I3, through the armature andleft-handV or marking contact of relay 4, through resistance I4, to thenegative terminal of battery I which is grounded. If ground isconnectedl from loop repeater YI to hub circuit I, to which the bottommain transmitting conductor '4l is connected, current will flow throughthe bottom windings of relays 4 and 5. The ei- 'fect of this `currentpreponderates over the effect of the current flowing in the top orbiasing windings 'of relays 4 and 5 and the armatures of 'these relaysare actuated to engage their spacing contacts. When the armatures `ofrelays r4 and 5 interference.

are thus' operated, the connections of battery I5 are reversed so thatground, instead of being connected to the top conductor extending to theright of the ligure, is connected to the bottom conductor, and positivebattery, instead of being connected to the bottom conductor, isconnected to the top conductor.V This reversal of battery transmits aspacing signal to the distant terminal.

Signals from the distant station are received over the lower pair ofconductors extending to the right of Fig. 1. The path may be tracedvfrom ground through battery 50, resistance 5I, righthand contact andarmature of relay 52, over the top conductor of this pair through theWinding ofinduction coil I1, the top winding of relay- I8, throughthe-bottom conductor of the pair and through the armature and left-handcontact of relay 53, back to ground at the. distant station. The eiectofcurrent for marking and spacing signals in the path just traced is toactuate the armature of relay I8 between its opposingY marking andspacing contacts. The circuit through the bottom windings of relay I8will be described in detail hereunder. i 1

For full duplex operation, as has been described, relay-I is in theposition shown. The

circuit through the bottom winding of relay I6 is, therefore, open atthe rightand left-hand make contacts of replay I. When the armature ofrelay I8 isron its left-hand or marking contact, a circuit may be tracedfrom negative bat- Y tery through resistance I9, the left-hand ormarking Contact and armature of relay I8, through resistances 20 and 2|and the top winding of relay II) to ground. This maintains the armatureof relay IIJ in engagement with its lefthand or marking Contact. Whenthe armature of relay I8 is actuated to engage its right-hand or spacingcontact, positive battery through resistance 22 is substituted fornegative battery through resistance |19 and the armature of relay I isactuated to engageits right-hand or spacing contact.l When the armatureof relay Il] is actuated to engageits spacing contact, ground isconnected to the armature of relay I0 and a spacing signal istransmitted over conductor 46 into the leg associated in the hub 2circuit. As the armature of relay I0 is actuated between its marking andspacing contacts, marking and spacing signals will be transmitted intothese circuits forming the receiving hub circuit.

It should be apparent from the above that for the full duplex conditiontwo hub circuits are connected to the left-hand side of Fig. 1. Signalsfrom one hub circuit,hub I, which serves as the transmitting hub,reverse the connections of battery I5 to transmit signals over the toppair of conductors extending toward the right of Fig. 1 to the distantstation. Signals received from-the distant station operate relay I8,which in turn operates relay I', which alternately connects negativebattery and ground to hub point 2, which is the receiving hub.. Thetransmitting and receiving circuits are independent. Signals may betransmitted from one hub circuit connectedV at the left to the distantstation connected at the right of Fig. 1, while signals are beingYreceived from the distant station and impressed upon the receiving hubcircuit without The circuit of Fig. 1., therefore, will function as afull duplex circuit .in conjunction with two connected hub circuits.

HALF DUPLEX OPERATION Refer to Figs. 1 and2.

When the circuit of this invention is to function as half duplexrepeater, ground is connected in the leg multiple circuit of Fig. 2 toconductor 48 through the contacts 54 of a relay in the leg multiplecircuit. A circuit may then be traced from ground through contacts 54,through conductor 48 from Fig. 2 into Fig. 1, through the winding ofrelay I to battery, operating relay I. This breaks the circuit extendingfrom hub I through the bottom transmitting conductor 41 and resistance23, at the right-hand break contact of relay I. As has been explainedabove, when the circuit per Fig. 1 functions half duplex, it isconnected to but one hub circuit. This is indicated as hub circuit 2,which is connected to conductor 46. Conductor 41 serves no purpose inhalf duplex operation. When relay I is operated, a circuit may be tracedfrom hub 2 through conductor 46, through the armature and left-hand ormarking contact of relay I0, which relay is operated, through theleft-hand armature and left-hand make contactv Vof relay I,

through the bottom winding-of relay I0, through4 the right-hand makecontact and armature of relay I, through the bottom windings of relays 5and 4, through resistances 1 and 6 and through battery 2 to ground. InFig. 2, three subscribers station circuits, each including atransmitting key and a telegraph sounder, are connected by means ofindividual loop circuits, individual inverse neutral telegraph repeatersand individual legs to hub 2. The circuits are shown in the markingcondition. All three of these circuits are identical. The circuitconnecting the subscribers station A, in the upper left-hand corner ofFig. 2 to hub 2, may be traced from positive battery in the toprectangle, marked loop repeater A, through the lower loop conductor 3,through the transmitting key contacts, or the switch shunting them, atsubscribers station A, the winding of the receiving magnet, the top loopconductor 4, the top winding of receiving relay I in loop repeater Aandthrough the armature and left-hand or spacing contact of transmittingrelay 2 to negative battery. Attention is called to the fact that theopposite ends of this loop, when the armature of relay 2 is inengagement with its left-hand or markingcontact, are connected tobatteries arranged in series-aiding relationship. The eiect of currentilowing through the top winding of relay vI for this condition tends toactuate the armature of relay I to engage with its left-hand or markingcontact as shown. This eiect preponderates over the eiTect of currentowing from negative battery, connected to the left-hand or markcontactof relay 2, through the armature of relay 2 and the bottom winding ofrelay I, to ground, tending to actuate the armature of relay I to engagewith its right-hand or spacing contact, and the armature of relay I ismaintained in engagement with its left-hand or marking contact.

The armature of relay 2 in loop repeater A, is

held in engagement during the marking condition, with its left-handcontact, by the eiect of current flowing from negative battery throughthe bottom winding of relay 2 to ground. The effect of this current isunopposed,`as no current flows through the top winding of relay 2 duringmarking. The path through the top winding of relay 2 extends fromnegative battery through the top winding of relay 2, through the 75left-hand or marking contact and armature of relay I in loop repeater A,over conductor 5 and through a concentration jack circuit, indicatedschematically by small circles joined to conductor v5, to hub 2.

Subscribers station B, shown at the left center of Fig. 2 andsubscribers station C shown at the lower left of Fig. 2 are each joinedto the hub 2 in the same manner as is subscribers station A. For themarking condition leg 6, joining hub 2 with loop repeater B and leg Ijoining hub 2 with loop repeater C are each terminated in negativebattery connected to the top winding of its respective relay 2 in looprepeater B and loop repeater C, respectively. It has been shown that leg46 which joins hub 2 with the inverse neutral repeater of the four-wiretrunk circuit per Fig. 1 is also terminated in negative battery 2 inFig. 1. l

For the marking condition, therefore, for halfduplex operation, underwhich arrangement Fig. 1 and Fig. 2 are interconnected, all legsrediating from the single hub which is used, in this case hub 2, areterminated in negative battery of the same magnitude so that no currentis transmitted through any of the legs such as 5, 6, 1 or 4,6 comprisingthe hub circuit.

If a spacing signal is to be transmitted from any one leg to all of theother legs, ground is connected to the one leg which is to transmit andcurrent ilows from negative battery connected to the ends of each of theother legs, toward and through hub 2, to the single ground connection onthe transmitting leg. Thus, if a spacing signal is to be transmittedfrom subscribers station A, the subscribers loop is opened. To do this,first the switch shunting the transmitting key is opened, so that thetransmitting key takes control of the loop. When the transmitting key isopened, the loop isrbroken. The top winding of relay I in loop repeaterA is deenergized. The armature of relay I is actuated so as to engageits right-hand or spacing contact which connects ground to leg conductor5. A sending relay, relay 2, in each of the other station legs isenergized as a result of this operation. A pair of sending relays,relays 4 and 5, in the trunk are operated to transmit a spacing signalto the distant central terminal. In the case of the station loops, theeiect of current flowing from negative battery through the top windingof relay 2 of repeater B as well as through the top winding of relay 2of loop repeater C, which eiect tends to actuate the armatures of eachof these relays to engage with theirV respective right-hand or spacingcontacts, preponderates over the eiect of lthe current through thebottom winding of each relay 2 and the armature of each of these relaysis actuated so as to engage with its right-hand or spacing contact. Thisconnects battery of the same polarity and magnitude to each -end of theloop of station B and station C. As a result of this, current ceases toflow in each loop and the receiving magnet at each station isdeenergized resulting in a spacing signal at each station.`

In the case of the four-wire trunk connected to hub 2 by means ofconductor 46, the eiect of current through the bottom winding of relays4 and 5 preponderates over the eiect of current through the top windingstending to hold the armatures of relays 4 and 5 on their markingcontacts, as shown, and the armatures of relays 4 and 5 will be actuatedto engage with theirY other or spacing contacts. 4This reverses theconnectionsof battery I to the top or transmitting loop of Fig. 1 andresults in the trans--l mission of a spacing signal vto the distantcentral terminal.

It has been described that the effect of current owing through the topwinding of relay 10, from battery through resistance I9, is to tend tohold the armature of relay II) in engagement with its left-hand ormarking contact. When signals are received from the hub circuit duringhalf duplex operation, as described above, no current will pass throughthe bottom winding of relay I0 for the marking condition. The eiect Vofcurrent flowing for the spacing condition is to augment the effect ofcurrent flowing through the top winding of relay I6, so that thearmaturev of relay I0 will be maintained in engagement with itsleft-hand or marking contact, as shown, while signals are being receivedfrom the hub circuit connected at the left of Fig. 1.

When signals are received from the distant terminal at the right, relayI8 will be actuated as described above under Full duplex operation. Forthe marking condition, bothV sides of the bottom winding of relay I0 areconnected to negativef battery, namely, battery 2 and negative batteryconnected from the loop repeater to each of the legs radiating from thehub circuit. The bottom winding of relay I0 will therefore bedeenergized. Relay I0 will, therefore, follow relay I8. For the markingcondition of relay I, negative battery 2 will be connected throughrsistances B and 1 and the Ibottom windings of relays 4 and 5, throughthe right-hand make contact and ,armature` of relay. I, through thelower winding of relay I0 and the leftehand make contact and armature ofrelay I to the lefthand contact and armature of relay I0 and over lead46't0 hub 2. For the .spacing condition, ground will be connectedthrough the right-hand contact and .armatureV of relay. Il) over vlead48 to hub 2. All of the\receiving relays in the various legs connectedto hub 2 will be actuated in response to the operation of relay I0.

' From the above, it should be apparent that, :for half l duplexoperation, a single hub circuit is connected to the repeater per Fig. 1.When signals are transmitted from 'the hub, Ybattery I5 will bereversed, through the operation of relays 4 and 5, to transmit thesignals to the distant station at the right. Signals received from thedistant station will actuate relay I8, which will in turn actuate relayIB, which will connect negative battery and ground to conductor 46extending to the left of Fig. l, to actuate receiving relays on thevarious legs of hub circuit 2.

If, during half duplex operation, it isdesired to break while thecircuit per Fig. 1 is receiving signals from the distant terminalconnected to the right of Fig. 1, any station connected through a leginto the hub at the left of Fig. 1 may actuate a relay connectedindividually in its respective leg, so as to transmit a spacing signalfrom the hub toward Fig. 1. Ground will be thereupon vconnected from theloop repeater associated with' the particular station. Current iiowingthrough the bottom winding of relay I0 in response to this ground willmaintain the armature of relay I0 in engagement with its left-hand ormarking contact, as soon as it has been operated to engage that contactin response to the next marking signal received from the distantterminal connectedto the right of Fig. 1, and current flowing throughthe bottom windings of relays 4 and 5 in response to the spacing signalfrom the hub, when relay I0 is held on marking, will actuate thearmatures of relays 1I and 5 so as to transmit a spacing signal to thedistant terminal at the right. If signals are beingl transmitted fromthe hub circuit -connected at the left of Fig. 1 to the distant terminalconnected atthe right of 1 and the receiver at the-right wishes tobreak, a spacing signal is impressed through the bottom pair ofconductors extending tothe right lof Fig. 1. In response to this, thearmature of relay I8 will lbe'actuated to engage its right-hand orspacing contact. As soon as the next marking signal is transmitted fromthe hub circuit, since no current will be owing through the bottomlwinding of relay I0, the armature of relay I0 will be actuated to engageits right-hand or spacing contact. The armature of relay I0 will bemaintained in this position since the path through the bottom winding ofrelay I0 is broken and the spacing current from the spacing contact ofrelay I8 will continue its elect of holding the armature of relay I0 inengagement withA its spacing contact. While this condition prevails, thepath extending from the hub circuit through the bottom windings ofrelays '4 and `5 remains open at the left-hand armature and contact ofrelay I0, so that no signals may be transmitted from the hub circuit tothe distant lterminal at the right. Meanwhile the ground connected tothe Aarmature of relay IIJ will maintain all of the legs connected tothe hub circuity in the spacing condition as a breaking signal. v l

VIBRATING CIRCUIT The wave shape of the signals received from thedistant terminal through the top Winding of relay I8 is usuallyV verymuch rounded in charac'- ter and would result in considerable distortionwere it not for the use of the vibrating circuit, which is connectedVthrough the two bottom windings of relay I8.

The vibrating circuit consists of two branches'. One branch extends fromground through the' middle winding of relay I8 and resistance 25,through resistance 2l to the armature of relay I8. 'I'he second branchextends from ground through the bottom winding of relay I8 and condenser26 through resistance 2'I to the same armature. When the armature ofrelay I8 is in' engagement with its left-hand or marking contact, thecircuit is extended through resistance I9 and negative batteryto ground.When the armature of relay I8 is in engagement with its right-hand orspacing contact the circuit` is extended through resistance 22 andpositive battery to ground.

The circuit is arranged so that when no current is traversing the topVwinding of relay I8, the armature ofrela'y I8` will vibrate continuouslyat a frequency fixed by the values of the inductance capacitance andresistance in the circuit and also by the adjustment of the relayitself. This vibrating circuit accelerates the action of the relay andvresults in retransmitting the signals received from the distantterminalconnected to the right-hand side of Fig. 1 to the hub circuitconnected to the left-'hand side of Fig. 1 with a minimum of distortion.The vibrating circuit is so arranged that the current through the middlewinding of relay I8 is in a direction to move the armature from thecontact to which it is held by the current in the top winding of therelay. When a reversal of current takes place at the distant end of theline and the line current falls to a point where the ampere turns of theline windings are less than the ampere turns of the middle vibratingwinding, the armature moves to the opposite contact. During the traveltime a discharge current from condenser I 26 through the bottom andmiddle windings in series aiding tends to accelerate the action. VWhenthe armature engages the opposite contact, the charge on condenser 26,which is in seriesvwith the bottom winding, is reversed. Since thebottom winding is poled opposite to the middle winding the chargingcurrent causes the contact just made to remain closed until the currentin the top winding builds up suil'iciently to maintain the contactclosure. At the same time the current in the opposing middle winding isalso building up.v When the charging current dies down and the currentsin the top winding and the middle winding have been established, thecurrent in the middle winding is again in such a direction as to movethe armature to the opposite contact when the line current loses controlof the relay. The above operation takes place each time a contact ismade.

OTHER MISCELLANEOUS KYllnn'iUi-nss INCLUDED IN CmcUrr A-MomtoriugProvision is made for lining up the circuit with a special test circuit.'Ihe function of jack 30 is to enable the test circuit to be connectedto the circuit herein. This testing circuit forms no part of thisinvention and its operation is not therefore described.

B-Noz'se killers Noise killers are connected to the transmitting circuitextending from the circuit herein to the distant terminal to the right.It consists of repeating coil I I, induction coils I2 and I3 and con- Anoise killer may be connected in the circuit,

incoming from the distant terminal connected to the right of Fig. 1.Coil I1 is usedffor this purpose. Its function is to reduce telegraphthump caused by induction of the vibrating circuit current into thereceiving end of thefincoming circuit through the windings of relay I8.

C-Contact protection Contact protection is provided across the contactsof relays 4, and I8 to reduce contact erosion. The contact protectionfor relay 4 consists of resistances 30 and 37| and condensers 32 and 33.The contact protection for relay 5 consists of resistances 34 and 35 andcondensers 36 and 31. 'I'he contact protection for relay I8 consists ofresistances 38 and 39 and condensers 40 and 4I.

D-Leg circuit waveshapers Wave Shapers are connected with the legs eX-tending to the two hub circuits connected to the left-hand end ofFig. 1. The function of the wave Shapers is to compensate for thearmature travel time of the relays transmitting to the leg circuits. Thewave shaper for the top conductor consists of condenser 42 andresistance 43. The wave shaper for the bottom conductor consists ofcondenser 44 and resistance 45.

What is claimed is:

`1. In a telegraph system, a repeater circuit, means in said circuit foroperably interconnecting a single group of telegraph circuits arrangedin a single inverse neutral concentration to a four-wire telegraphcircuit at a rst time, means in said circuits for operating saidcircuits on a half duplex basis at said rst time, means in said repeatervfor operably interconnecting two groups ofY telegraph circuits arrangedin two inverse neutral concentrations to a four-wire telegraph circuitat a second time, and means in said circuits for transmitting a separatecommunication through each of said two concentrations simultaneously atsaid second time.

2. A system in accordance with claim 1 including relay means forswitching said repeater from half duplex operation through oneconcentration, to simultaneous separate communications through said twoconcentrations.

3. A system in accordance with claim 1, including breaking means for usewhile the system is conditioned for half duplex operation.

4.- A system in accordance with claim 1 including a relay in saidrepeater having a winding in series in a conductor connected to the hubof one of said inverse neutral concentrations.

5. A system in accordance with claim 1, including'an individual windingon each of two relays, said windings'being connected in series in aconductor connected to the hub point of one of said inverse neutralconcentrations.

' 6. A system in accordance with claim 1, having a winding on a relay insaid repeater in series in a conductor extending to the hub of one ofsaid inverse neutral circuits, and an armature cn a second relay in saidrepeater, said armature being connected in `series in the conductorconnected to the hub of the other of said inverse neutralconcentrations.

7. A system in accordance with claim 1, including a iirst two wires ofsaid four-wire circuit arranged for transmitting from an inverse neutralcircuit and a second two wires of said fourwire circuit arranged fortransmission toward an inverse neutral circuit, and means for reversingthe polarity of a battery connected in series in said rst two wires forthe transmission of marking and spacing signals from said inverseneutral circuit.

8. A system in accordance with claim 1, having a winding of a receivingrelay in series with two conductors of the four-wire circuit, said relaybeing conditioned to transmit polar telegraph signals through a windingon an auxiliary receiving relay, said auxiliary relay being conditionedto impress inverse neutral telegraph circuits'on one of said inverseneutral concentrations.

9. Ina system in accordance with claim 1, an auxiliary receiving relayin said repeater responsive to a primary receiving relay in the tworeceiving conductors of said four-wire circuit, said auxiliary receivingrelay being conditioned toimpress inverse neutral signals on an inverseneutral concentration, and breaking means connected to said auxiliaryreceiving relay under control of either the four-wire circuit or anotherinverse neutral circuit in said concentration when either is in thereceiving condition, to stop further transmission from an'associatedtransmitting station.

10. In a telegraph system, a telegraph repeater for interconnectinginverse neutral telegraph circuits to a four-Wire telegraph circuit, andmeans in said repeater for transmitting two separate communicationsbetween said inverse neutral circuits and said four-Wire circuitsimultaneously.

11. In a telegraph system, a telegraph repeater, means in said repeaterfor repeating inverse neutral telegraph signals from a first inverseneu-

